With the proliferation of various communication and entertainment technologies, it is becoming increasingly desirable to receive signals in moving vehicles. Today's vehicles sometimes receive radio, wireless telephone signals, email, electronic data, Global Positioning Satellite (GPS) data, television signals, etc. This need for in-vehicle reception exists in consumer automobiles, commercial automobiles and trucks, commercial and private airplanes, pleasure and commercial boats, and in military vehicles of all sorts, just to name a few. For many of these applications, it would be desirable if the signals could be received using a rather unobtrusive antenna. At the same time, it can be desirable to use a large, somewhat narrow beam antenna, as opposed to a small, wide beam antenna, in order to be able to pick up signals from rather remote sources (which can be faint).
Moreover, in order to collect the faint signals from the remote sources, often it is necessary to keep the antenna pointed at the source. Unfortunately, the movement of a vehicle makes it difficult for a typical antenna to track a signal source. The antenna could be made to track side-to-side (azimuth) and up and down (elevation), but if the antenna is of substantial size, this has disadvantages. One such serious disadvantage is that the antenna might then protrude significantly at times, interfering with the smooth airflow over the vehicle or adversely affecting the aesthetics of the vehicle.
In military radar applications for aircraft, it has been known to utilize an array of antenna elements and to mechanically rotate the array in azimuth to provide wide side-to-side coverage. To provide wide up and down (elevation) coverage, the radar array is electronically controlled to “look” in a wide variety of elevation directions (to scan in elevation without moving the antenna elements physically). The electronic control consists of applying phase shifts to the incoming electromagnetic energy received at the various antenna elements to cause the energy received from a desired direction to add up constructively, allowing the array to “see” in that direction. Unfortunately, the electronic hardware typically needed for such scanning by applying varying phase shifts is rather expensive, limiting the practical application of such antenna arrays to military or similar applications.
In recent years, Earth-orbit satellites have been launched to provide digital television signals directly to peoples' homes. These satellites are called Direct Broadcast Satellites (DBS). Typically, the satellite is placed into a geosynchronous (stationary) orbit around the Earth. As such, in order to receive the television signals at a building or home, a small antenna dish typically is mounted to the building or to a nearby mounting pole and is aimed at the satellite. These small antenna dishes are concave and are about the size of a pizza pan.
While such dish antenna designs are useful for receiving the DBS signal at a building, these antennas are especially ill-suited for use on a moving vehicle. This is so because this type of dish antenna presents a rather large profile, which can interrupt smooth airflow as the vehicle travels. Indeed, the dish antenna is large enough and has a large enough profile that wind resistance and noise generated thereby would be very objectionable if one were to mount the dish antenna to the outside of the vehicle. Moreover, because of the large profile of the dish antenna, mounting this antenna securely enough to maintain a stable position despite wind resistance presents a formidable challenge.
As mentioned above, mounting a dish antenna to a vehicle presents an additional challenge in the difficulty of keeping the antenna trained on the satellite. The reason for the difficulty is that the vehicle changes orientation in use. One moment the vehicle is oriented in one direction and at another moment the vehicle can be turned to be pointing in a very different direction. For example, in order for a vehicle-mounted DBS antenna to be useful, it would need to be able to be trained on the satellite and generally stay pointed at the satellite regardless of changes in orientation of the vehicle. To accomplish this with a dish antenna would mean rotating the dish and/or changing the elevation angle of the dish. In general, this is impractical.
Accordingly, it can be seen that a need remains in the art for a low-cost directional antenna which can be mounted to a vehicle for receiving signals, which antenna has a low profile, and which can be trained on a source and continue to point at the source as the vehicle changes orientation. It is to the provision of such an antenna that present invention is primarily directed.